Primary 5 Science Systems Quiz

Primary 5 Science Quiz - Systems (Answer Key)

Total Marks: 40

Section A: Multiple-Choice Questions (10 marks)

1. Answer: A [1]
Explanation: Air enters through the nose, passes down the trachea (windpipe), branches into the bronchi (one to each lung), enters the lungs, and finally reaches the alveoli (air sacs) where gaseous exchange occurs.

2. Answer: B [1]
Explanation: The pulmonary vein carries oxygen-rich blood from the lungs to the left atrium of the heart. The pulmonary artery carries deoxygenated blood from the heart to the lungs. The aorta carries oxygenated blood from the heart to the body. The vena cava carries deoxygenated blood from the body to the heart.

3. Answer: B [1]
Explanation: Xylem transports water and mineral salts from roots to leaves. Phloem transports food (sugar) from leaves to other parts. In a dicot stem cross-section, xylem is on the inner side of the vascular bundle, phloem on the outer side.

4. Answer: D [1]
Explanation: In a series circuit, there is only one path for current. If one bulb fuses, the circuit is broken (open circuit), and current cannot flow. All bulbs go out.

5. Answer: C [1]
Explanation: The human heart has four chambers (two atria, two ventricles). Valves prevent backflow of blood. Arteries carry blood away from the heart; the pulmonary artery carries deoxygenated blood. The pulmonary vein carries oxygenated blood.

6. Answer: C [1]
Explanation: In a bulb, electrical energy is converted to both light energy and heat energy. Some electrical energy is always "lost" as heat.

7. Answer: B [1]
Explanation: Phloem transports food (sucrose/glucose) made during photosynthesis from leaves (source) to other parts of the plant (sinks) like roots, fruits, and growing shoots.

8. Answer: C [1]
Explanation: Gaseous exchange (oxygen in, carbon dioxide out) occurs in the alveoli, which have thin walls and a rich blood supply. The trachea and bronchi are air passages; the diaphragm is a muscle for breathing.

9. Answer: C [1]
Explanation: In a parallel circuit, each bulb has its own path to the battery. Removing one bulb breaks only that branch; the other bulb still receives the full voltage and remains at the same brightness.

10. Answer: A [1]
Explanation: Deoxygenated blood: Right atrium → Right ventricle → Pulmonary artery → Lungs (gets oxygenated) → Pulmonary vein → Left atrium → Left ventricle → Aorta → Body.

Section B: Short-Answer Questions (10 marks)

11.
(a) Stomach [1]
Most chemical digestion (especially of proteins) begins in the stomach with gastric juices, though the small intestine completes digestion of all food types.

(b) Small intestine [1]
The small intestine (specifically the ileum) has villi and microvilli that greatly increase surface area for absorption of digested nutrients into the bloodstream.

12.
(a) Both Bulb B1 and Bulb B3 will not light up (go off). [1]

(b) In a series circuit, there is only one path for current. When Bulb B2 fuses, the circuit becomes open/broken, so current cannot flow through any part of the circuit. [1]
Key concept: Series circuit = single loop. Break anywhere stops current everywhere.

13.
(a) Carbon dioxide [1]
Change: from 0.04% to 4% (increase of ~3.96%). Oxygen changes from 21% to 16% (decrease of 5%). While oxygen has a larger absolute change, carbon dioxide shows the greatest relative change (100-fold increase). At P5 level, either "carbon dioxide" (greatest relative change) or "oxygen" (greatest absolute change) may be accepted depending on school marking scheme. Most P5 papers accept carbon dioxide as the answer for "greatest percentage change" meaning relative change.

(b) Nitrogen is not used by the body in respiration. It is an inert gas that is simply breathed in and out unchanged. [1]
The body does not absorb or produce nitrogen during gaseous exchange.

14.
(a) Xylem [1]
Xylem transports water and mineral salts from roots to leaves. In the leaf vascular bundle, xylem is typically on the upper side.

(b) Stomata [1]
Stomata (singular: stoma) are tiny pores on the leaf surface (usually lower epidermis) that open and close to allow gas exchange (CO₂ in, O₂ out) and transpiration (water vapour out).

15.
(a) Object X is a conductor of electricity. [1]
Since the bulb lights up, the circuit is complete, meaning electric current can flow through Object X.

(b) Plastic is an insulator (non-conductor) of electricity. It does not allow electric current to pass through, so the circuit remains open and the bulb does not light up. [1]
Conductors (metals) allow current flow; insulators (plastic, wood, rubber, glass) do not.

Section C: Structured / Open-Ended Questions (20 marks)

16.
(a) Labels on diagram: Pulmonary artery (from right ventricle to lungs), Pulmonary vein (from lungs to left atrium). [1]
Check: Pulmonary artery carries deoxygenated blood; pulmonary vein carries oxygenated blood.

(b) Blood in the pulmonary artery is deoxygenated (low in oxygen, high in carbon dioxide), while blood in the pulmonary vein is oxygenated (high in oxygen, low in carbon dioxide). [1]
Accept: "Pulmonary artery carries deoxygenated blood to lungs; pulmonary vein carries oxygenated blood from lungs."

(c) The left ventricle pumps blood to the whole body (systemic circulation), which requires higher pressure to overcome the longer distance and greater resistance. The right ventricle pumps blood only to the lungs (pulmonary circulation), which is a shorter distance with lower resistance. Thicker walls generate stronger contractions for higher pressure. [2]
Mark breakdown: 1 mark for "left ventricle pumps to whole body / needs higher pressure", 1 mark for "right ventricle pumps only to lungs / lower pressure needed".

17.
(a) Xylem and Phloem [1]

(b) Xylem: Transports water and mineral salts from roots to all parts of the plant (one-way, upward).
Phloem: Transports food (sugar/sucrose) made in the leaves during photosynthesis to all parts of the plant (two-way, up and down). [2]
Mark breakdown: 1 mark for xylem function, 1 mark for phloem function. Must mention direction for full marks.

(c) Root hairs increase the surface area of the root for absorption. They are long, thin extensions of root epidermal cells that penetrate between soil particles, allowing more contact with water and dissolved mineral salts. [1]
Key concept: Surface area → rate of absorption.

18.
(a) Circuit B [1]
Circuit B has 2 batteries (3V) and 1 bulb → highest voltage across a single bulb → brightest.

(b) Circuit C [1]
Circuit C has 2 batteries (3V) but 2 bulbs in series → voltage shared (1.5V each) → dimmest. (Circuit A has 1 battery (1.5V) and 1 bulb → same brightness as each bulb in Circuit C.)

(c) Brightness depends on voltage across each bulb (and thus current through it).

• Circuit B: 2 batteries in series = 3V across 1 bulb → highest voltage → highest current → brightest.
• Circuit C: 2 batteries = 3V total, but shared equally by 2 identical bulbs in series → 1.5V per bulb → same as Circuit A (1 battery, 1 bulb) → dimmer than Circuit B. [2]
  Mark breakdown: 1 mark for explaining Circuit B (higher voltage per bulb), 1 mark for explaining Circuit C (voltage shared in series).

19.
(a) During inhalation: The diaphragm contracts and flattens (moves down). The ribs move up and out (expanding the chest cavity). [2]
Mark breakdown: 1 mark for diaphragm action, 1 mark for rib action.

(b) These actions increase the volume of the chest cavity (thoracic cavity). This decreases the air pressure inside the lungs below atmospheric pressure. Air from outside (higher pressure) rushes into the lungs (lower pressure) to equalise the pressure. [2]
Mark breakdown: 1 mark for "volume increases → pressure decreases", 1 mark for "air moves from high to low pressure / into lungs". Key physics: Boyle's Law (simplified).

20.
(a) Number of batteries (in series) [1]
The variable that is deliberately changed by the investigator.

(b) Brightness of the bulb [1]
The variable that is measured/observed in response to the change.

(c) Any two of:

• Type/voltage of batteries (use identical batteries)
• Type/rating of bulb (use identical bulbs)
• Length/thickness of connecting wires
• Temperature of surroundings
• Position of bulb in circuit (always series) [2]
  Mark breakdown: 1 mark each for any two valid controlled variables. Must be variables that could affect brightness if changed.

Marking Notes for Teachers:

• Accept scientifically correct alternative phrasing.
• For diagram labelling questions, award marks only if labels are correctly placed.
• For explanation questions, key concepts/keywords must be present for marks.
• Common misconceptions to watch for:
  • Q4/Q12: Thinking current "starts" at battery and bulbs "use up" current (current is same everywhere in series).
  • Q9: Thinking parallel bulbs share current like series (voltage is same across parallel branches).
  • Q16(c): Saying left ventricle is thicker because it's "bigger" rather than "pumps to whole body/higher pressure".
  • Q19: Saying "diaphragm expands" instead of "contracts and flattens".
  • Q20: Confusing independent/dependent variables.